faculty spotlight

Kirk Personius, PT, PhD

Kirk Personius, PT, PhD, is a clinical associate professor with
UB’s Department of Rehabilitation Science and the Doctor of
Physical Therapy program director.

His research focuses on how nerve and muscle interact during
development, aging and disease. Currently, he is studying the role
of the nervous system in muscle atrophy and how nerve activity
influences neuromuscular development.

The Role of the Nervous System in Muscle Atrophy

Through this project, Personius is studying the role of motor
neuron innervation in sarcopenia, the loss of muscle mass and
function during aging. Muscles depend on innervation—being
connected to the musculoskeletal nervous system—to maintain
function. A well-studied example of a breakdown in the
neuromuscular system is the muscle atrophy seen in Bell’s
palsy following damage to the facial nerve. If a muscle fiber loses
the connection to its nerve—it has only one—it
withers.

The area that Personius is investigating is not muscle fiber,
but the neuromuscular junction, the connection between the nervous
system and muscle where nerve signals arrive and stimulate actions.
He is looking at how the connection is maintained in working
condition and whether it is failure at the connection that is the
chief culprit in the loss of muscle function in sarcopenia.

Personius has shown that a particular receptor in neuromuscular
junction—the tyrosine kinase B (TrkB) receptor—may be a
key to a sequence of molecular events that lead to muscle atrophy.
TrkB—called “track-B”—is a kind of dock for
particular proteins called neurotrophins that are messengers in a
repair and regulation system that keeps cells healthy and
functioning. He has found that reducing the number of TrkB
receptors in a neuromuscular junction by half causes changes in the
junction that resemble changes caused by aging. Reducing the number
of TrkB receptors leads to a spreading apart of another set of
receptors that “hear” signals from the motor nerve; the
function of the neuromuscular junction then starts to show fatigue,
and the muscle begins to atrophy.

Personius says that practical implications from this research
suggest that if a way can be found to maintain TrkB receptor
quantity, that may, in turn, maintain the neuromuscular junction
and the muscle fiber it controls.

“Muscle is ultimately dependent upon nervous input to
function, so studying muscle independent of the nervous system is
problematic,” he said. “Understanding how the
neuromuscular system ages will help us to prevent loss of muscle
function in senescence.”

How the Nerve-Muscle System Develops

In related research, he is looking at how the nerve-muscle
system develops. When we’re born, we have multiple nerves
connected to each muscle fiber; during the first few months of
life, those connections are reduced to one nerve for each muscle
fiber, a process called synapse elimination. Personius has
shown that the pattern and amount of nervous activity is important
in this pruning process. Personius is currently working on
understanding the molecular mechanisms underlying this sorting of
neurological connections.

“We know that nervous activity influences which
neuromuscular connections are maintained and which are permanently
eliminated,” he said. “What we don’t know are the
molecular mechanisms by which the muscle ‘listens’ to
the nervous activity and chooses to support one connection and
delete the other. This is what we are trying to understand
now.”

Research Opportunities for Students

Personius welcomes PhD and master’s students from the
rehabilitation science, neuroscience and exercise science programs,
as well as undergraduate University Honors students, to his lab for
research collaboration.